How did Romeo and Juliet get bad advice from their elders (mainly the Nurse and Friar Lawrence)?

After Lord Capulet completely loses his temper and threatens to allow Juliet to beg and starve in the streets if she refuses his directive to marry the County Paris, Juliet's nurse -- a woman who has really always been on Juliet's side -- changes her tune and advises her to marry the count.  She says, "I think you are happy in this second match, / For it excels your first, or, if it did not, / Your first is dead, or 'twere as good he were / As living here and you no use to him" (3.5.235-238).  She says that she believes Juliet will be happy in the marriage to Paris, and even if she isn't it doesn't matter because her first spouse is as good as dead.  This turns out to be bad advice because it makes Juliet desperate.  She no longer feels as though she has any allies, and she is ready to do anything to escape her impending nuptials to Paris.

Juliet goes to Friar Lawrence, and when she threatens to kill herself, he says, "I do spy a kind of hope, / Which craves as desperate an execution / As that is desperate which we would prevent" (4.1.69-71).  He advises her to fake her own death so as to escape "this present shame," deceiving her parents and the entire community so that she can run away and be with Romeo in his exile (4.1.120).  This turns out to be bad advice when the letter acquainting Romeo with this plan cannot be delivered, and he arrives at Juliet's tomb to kill himself, thinking she is dead.  Although both the nurse and the friar mean well, their advice is not very good and helps to hasten the tragedy of the play.